Along with the development of Internet, a great many multimedia services emerge and people's demands on mobile communications are no longer limited to telephone and message services. At present, application services have been introduced into multimedia services. The feature of application services is that same data may be received by a plurality of users in the same time, for example: VOD (Video On Demand), telecast, video conference, online education and interactive games.
In order to effectively use the resources of mobile networks, Multimedia Broadcast Multicast Service (MBMS) technology was introduced. The MBMS is a Point-To-Multipoint service in which a data source sends data to a plurality of users. Through this service, the sharing of network resources can be realized, including the sharing of mobile core network and access network resources, particularly the sharing of air interface resources. Further, the MBMS in 3GPP not only can realize the multicast and broadcast of pure-text low-speed messages but also can realize the multicast and broadcast of high-speed multimedia services.
As the MBMS is a service catering for the whole network, a same MBMS may be established at different lower network element nodes. FIG. 1 is a flow chart of the method for synchronization processing of the MBMS in a plurality of network elements in the prior art, and the method includes the following processing.
S102, sending an MBMS data packet by the upper network element to the lower network elements. This data packet includes service data and time stamp information, data packet sequence number information and accumulated service data length information. The upper network element marks same time stamp information for one or a plurality of continuous data packets. These data packets marked with the same time stamp constitute a data burst or synchronization sequence. Particularly, the upper network element marks each data packet as a data burst or synchronization sequence. In this case, each data burst or synchronization sequence only contains one data packet.
S104, conducting RLC (Radio Link Control) protocol-layer tandem connection processing of the service data included in the data packets of a same data burst by the lower network elements, while no RLC tandem connection processing is conducted for the data packets of different data bursts. Moreover, when conducting the RLC protocol-layer processing of the data packets of a same data burst, the RLC sequence numbers in RLC protocol-layer will be reset starting from the first data packet of each data burst. That is to say, starting from the first RLC PDU (Protocol Data Unit) of the first data packet of each data burst, RLC sequence numbers will be distributed from a specified or configured fixed value. In the prior art, when a plurality of continuous data packets are lost during transmission from an upper network element to lower network elements, the lower network elements will be unable to judge the RLC PDU length occupied by the lost data packets during RLC processing, thereby the network elements of which packets are lost will be unable to maintain consistent with other network elements during the follow-up RLC processing. Like that, to reset the RLC sequence numbers at the beginning of each data burst may avoid the foregoing problem and guarantee the consistence of RLC sequence number of each network element at the beginning of each data burst.
S106, sending the data packets in turn for the service data included by the data packets of a same data burst by the lower network elements via a radio interface starting from the transmission time corresponding to the time stamp marked in the data packets. As the foregoing information sent by the upper network element to the lower network elements is identical, the lower network elements may conduct identical processing. In this way, the synchronous transmission of MBMS among the cells of the lower network elements is realized.
Currently, the time stamp information of each data packet may be set in the following two ways.
Way 1: The upper network element marks time stamps according to the receiving moments of data packets, and a same time stamp is marked for the data packets received within a specific length of time interval, wherein the specific length of time interval is called synchronization sequence length or scheduling period. Under this circumstance, the length of the scheduling period is equal to the length of the time stamp interval of the adjacent data bursts.
Way 2: The upper network element virtualizes the RLC protocol-layer processing of the lower network elements. According to the result of the virtualized RLC processing, the data packets which need to undergo RLC tandem connection processing are marked with a same time stamp. In this technology, the length of the scheduling period is the minimum value of the time stamps of the adjacent data bursts.
In view of the foregoing two setting methods, the time stamp information rests with the time when data packets arrive at the upper network element, so the time stamp intervals of the data packets are not fixed. It is supposed that the service data stream the upper network element receives are the data stream shaped based on QoS. In other words, in any period of time, bandwidth of the service data stream does not exceed the maximum bandwidth defined by QoS parameters, and it is supposed that the channel resources of the radio interface in the foregoing period of time match the QoS parameters.
An MBMS may be sent via a radio interface by means of Time Division Multiplex (TDM). The configuration of TDM contains the following parameters: TDM period, TDM offset and TDM repetition length. The TDM resources available to a service may be expressed as follows: (the result of System Frame Number (SFN) divided with no remainder by the number of 10 ms radio frames contained in a TTI) modulo (TOM period)=TDM offset+i, wherein i=0, 1, (TDM period−1). Specifically, an MBMS is sent in the distributed TDM period, for consecutive TDM repetition length of TTI (Transmission Time Interval) starting from the (TDM offset)th TTI. The maximum TOM repetition period is 9. The TTI length that may be used by MBMS is 40 ms or 80 ms. A service may be sent via a radio interface only within the available transmission time configured in the TDM period.
When data are sent by means of TDM, as the transmission time of an MBMS on a radio interface is discontinuous and appears cyclically and periodically according to the configuration of TDM. As the time stamps are uncertain in the current scheduling method, probably the time stamp information is unable to directly correspond to the initial time when the MBMS may be sent via the radio interface. That is to say, the time stamp and the radio interface transmission time (available transmission time) cannot form one-to-one correspondence. For example, the scheduling period and TDM period are not mutually matched as shown in FIG. 2.
FIG. 3 is a schematic showing inconsistent distribution of the resources to which different scheduling periods correspond. As shown in FIG. 3, in the TDM configuration mode, as the radio channel resources are discontinuous, the available radio resources in different locations at a same time period are different. In this case, the scheduling algorithm in the prior art will generate a wrong result. The data packets to be sent in a specific period of time supposed by the scheduling algorithm in the prior art might not be sent via the radio interface, and overflowing may occur. This will lead to the loss of service data and seriously impair service reception quality.